Data transmission in communication systems involve transmitting data packets and control information, wherein the control information indicates a manner of decoding the data packets. In wireless communication systems, the data packets and control information are channel coded to compensate for errors arising in their transmission to a receiver. The control information can be transmitted over a same communication channel with the data packet as a header or over a different communication channel parallel to the communication channel of the data packet transmission. Regardless of the manner in which the control information is transmitted, the data packet cannot be successfully decoded at the receiver if the control information cannot successfully decoded at the receiver.
Current proposals for data transmissions in wireless communication systems utilize a form of Automatic Retransmission Request (ARQ) referred to as Hybrid ARQ. In Hybrid ARQ, errors in data packet transmissions can be corrected using a technique known as Incremental Redundancy (IR), which involves combining two or more transmissions of the same data packet. IR, however, cannot be used to correct errors in control information transmissions because a separate control channel for the control channel would be needed. Thus, it is important that the control information be successfully decoded on each transmission attempt otherwise the data packet transmissions cannot be successfully decoded at the receiver.
One proposal for increasing the reliability of control information transmissions involves utilizing stronger channel coding. See FIG. 7, which depicts an example 70 utilizing stronger channel coding on the control information. In example 70, control information is transmitted as a packet header with the data over a same communication channel. The control information is channel coded at a rate of ¼, whereas the data is channel coded at a rate of ½. Thus, the control information is channel coded at twice the rate of the data packet, which increases the likelihood that the control information can be successfully decoded at the receiver. This proposal for utilizing stronger channel coding on the control information increases overhead, which is undesirable in wireless communication systems.
Another proposal for increasing the reliability of the control information transmission involves transmitting the control information on a parallel channel to the data packet transmission thereby allowing the control information transmission to be controlled independently of the data packet transmission to increase its reliability. FIG. 8 depicts an example 80 illustrating control information being transmitted over a parallel channel, wherein the channel over which the control information is transmitted is independently power controlled to increase the reliability of the control information transmission. In example 80, the control information and data packet transmissions both span a duration equivalent to a frame. In order to decode the data packet transmission, the receiver would need to wait at least the whole duration of the frame to receive and successfully decode the entire control information transmission. This proposal is undesirable because it would cause an increase in frame transmission delays when the control information transmission cannot be successfully decoded.
Accordingly, there exists a need for a method and apparatus of data transmission in which the reliability of control information transmission can be increased without increased overhead and frame transmission delays.